improve packageurlinterceptor errors

if it's going to prevent something to load, at least explain a bit what's
going on.

Reviewed by David Edmundson

src/plasmaquick/packageurlinterceptor.cpp

@@ -143,6 +143,7 @@ QUrl PackageUrlInterceptor::intercept(const QUrl &path, QQmlAbstractUrlIntercept
                 return path;
             }
         }
+        qWarning() << "WARNING: Access denied for URL" << path << m_package.path();
         return QUrl::fromLocalFile( allowedPaths.first() + "/org/kde/plasma/accessdenied/qmldir");
     }